1. Field of the Invention
This invention relates to a magnetic recording and/or reproducing apparatus in which a magnetic head is moved relative to a magnetic recording medium when magnetically recording or reproducing information.
2. Description of the Related Art
FIG. 1 is a perspective view to explain the structure of the cylinder and its associated parts of the rotary head device used in the magnetic recording and/or reproducing apparatus of this kind in the form of VTR.
In FIG. 1, reference character C denotes the cylinder of the rotary head device, around which the magnetic recording medium or magnetic tape 4 is wound by means of guide posts 23 and 24, as it runs, while sliding on the outer periphery of the cylinder C, by a tape drive system (not shown).
The cylinder C is constructed from a rotary drum (upper drum) 1 and a fixed drum (lower drum) 2. Both drums 1 and 2 are concentrically supported on a common fixed shaft 9 with a slit 3 therebetween.
The rotary drum 1 is rotated by an electric motor. As shown in FIG. 2 and FIG. 3, a magnetic head 5 is fixedly mounted in a recess 7 formed in the lower edge of the rotary drum 1, has a magnetic gap 8 and is arranged so that its tip 6 which is in sliding contact with the magnetic tape 4, i.e., the magnetic tape sliding surface (hereinafter abbreviated to the sliding surface) 6, projects radially outwardly of the outer peripheral surface of the rotary drum 1.
With such a construction and arrangement, during the recording or reproducing, the magnetic tape 4 is slidingly running under the condition that it is wound around the cylinder C, while the rotary drum 1 is rotating as shown in FIG. 1. Because it rotates together with the rotary drum 1, the magnetic head 5 is sliding on the magnetic tape 4 to effect the recording or reproducing.
By the way, at the time of the recording or reproducing operation of the VTR, rotation of the rotary drum 1 induces accompanying movement of air therewith in the vicinity of the surface of the rotary drum 1, because air has a viscosity. For this reason, a lubricating layer is formed with flow of air, intervening between the magnetic tape 4 and the rotary drum 1. Owing to this lubricating layer, a pressure is generated. By this pressure, the magnetic tape 4 is floated up from the outer peripheral surface of the rotary drum 1 to some extent.
Here, as helical scanning is performed, the width of that part of the magnetic tape 4 which confronts the rotary drum 1 varies with the angular position of the circumference of the drum. Therefore, the floating amount, or the height of floating, of the magnetic tape 4 from the rotary drum 1 is different with different angular positions of the drum. In a case where the magnetic head 5 and the recess 7 are not provided, the variation of the magnetic tape floating amount with the angular position is shown in FIG. 4. It is understood from this figure that the magnetic tape floating amount is larger on the magnetic head's advancing side of the drum, and becomes smaller on the head's receding side. Particularly at a portion in which the head recedes from the tape, the floating amount drops locally.
In an alternative case where the rotary drum 1 is provided with the magnetic head 5 and the recess 7, floating states of the magnetic tape in the neighborhood of the magnetic head are shown in FIG. 5(A) and FIG. 5(B). FIG. 5(A) shows the floating state of the tape on the head advancing side. FIG. 5(B) shows the tape's floating state on the head receding side.
Thus, in the conventional rotary head device, during the recording or reproducing, because the floating amount of the magnetic tape is large on the head advancing side, the magnetic tape gets a large spacing with respect to the magnetic head, causing the reproduced output to lower. On the head receding side, on the other hand, because the floating amount of the magnetic tape is small, the magnetic tape 4 comes into contact with the magnetic head 5, giving rise to some possibility of damaging the magnetic tape 4 and also to an unduly large wearing of the magnetic head 5. These produce problems of reducing the fidelity and durability.
Also, since the sliding resistance of the magnetic tape is unstable, the rotary drum rotates at uneven speeds. By this, the reproduced signal is disturbed, causing jitters to appear in the reproduced picture. Thus, there is another problem of deteriorating the quality of the picture. Further, since the recession of the magnetic head from the magnetic tape is accompanied with local dropping of the floating amount, this interaction with the magnetic tape induces vibrations of the magnetic tape. The spatial relationship of the magnetic head and the magnetic tape to each other in recording or reproducing the signals is disturbed at that time. Thus, yet another problem arises that turbulence occurs in the picture.